Fix Docker signup and document deploy, migrate, and rebuild flow.

Use FormData and server-side sign-in after register, trust proxy origins for reverse-proxy deploys, pass public URL build args in Docker, and clarify that git pull plus up -d --build is required to ship code and run pending migrations.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-compose.yml

@@ -2,6 +2,9 @@ services:
   app:
     build:
       context: .
+      args:
+        NEXT_PUBLIC_APP_URL: ${NEXT_PUBLIC_APP_URL:-http://localhost:3000}
+        BETTER_AUTH_URL: ${BETTER_AUTH_URL:-http://localhost:3000}
     image: beenvoice:local
     environment:
       NODE_ENV: production